textproduct: Rapid City

KEY MESSAGES

- Cool and wet this weekend, with daily precipitation in the region.

- Gradual warmup early next week.

DISCUSSION

(This Evening Through Friday) Issued at 213 PM MDT Fri Sep 18 2026

Current Water Vapor and upper air models show southwest flow over the forecast area, as upper low digs into the Rockies. 18Z surface analysis depicts a low over southeastern SD, with frontal boundary stretching into central Nebraska. Winds are generally light out of the north, with temperatures in the 60s to upper 70s.

Out ahead of the upper low, a disturbance will lift up into the region this evening. The line of showers/storms is currently in central Wyoming moving northeast, expected to enter the forecast area in a few hours. Generally light precipitation with the evening precipitation, but accumulations nearing a tenth of an inch may be possible in heavier precip cores. Precipitation may linger into the overnight hours, and some showery development is possible again during the day Saturday. There's a low-end chance for a severe storm Saturday afternoon, given some CAPE values 500-1000 j/Kb, however weak effective shear (20-30kts).

Attention then turns to the main event, as the upper low moves over Wyoming later Saturday into Sunday. Widespread precipitation is expected to move into the region over this timeframe. Heaviest amounts are expected Sunday morning and afternoon and will taper off from west to east Sunday night into Monday. LREF probabilities for 24 QPF 0.5" or more has a bullseye of 70-90% over the Black Hills into southwestern SD. Probabilities for 1" or more QPF range from 30-60% in the same area. Expect cooler temperatures as well as the low moves into the plains, with high temperatures Sunday only reaching around 60 over the plains, and the low to mid 50s over the Black Hills.

By the latter half of monday, the pattern changes again as upper ridging builds over the plains, bringing a gradual warming trend Monday through much of next week. Temperatures climb back to at or above normal by Tuesday and Wednesday.

AVIATION

(For the 00Z TAFS Through 00Z Saturday Evening) Issued At 534 PM MDT Fri Sep 18 2026

A cluster of thunderstorms will cross NE WY this evening into far western SD, and may have gusty/variable winds with it. Chances for precipitation will continue overnight into Saturday as a large system crosses the region. IFR/LIFR CIGS will return to the western SD plains late tonight and continue through Saturday morning. Areas of dense fog are also expected with LIFR VSBY. CIGS could see some gradual improvement through the day tomorrow but should still be limited to no higher than MVFR, especially if rainfall is accompanied.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.